Owing to the expense involved in the execution of GWA studies, it was sensible to perform the first studies in a set of closely related populations for which shared resources could be used. As a first step, a focused effort in which GWA studies of many phenotypes were conducted largely in the same populations — and even in the same samples — had several advantages over a dispersed effort that would have considered a larger diversity of populations. The focus on fewer populations aided the development of standard single-nucleotide polymorphism (SNP) panels ascertained for informativeness in detecting common risk variants in those populations. It facilitated the use of shared controls in large studies of multiple phenotypes, reducing the effort required in sample collection and genotyping. Finally, it led to the collection by separate investigators of commensurable samples, enabling large meta-analyses with closely related populations.
